A device is disclosed for controlling a rate of gas pressure increase generated by a propellant for propelling a projectile from an upstream towards a downstream end of a gun barrel. The device includes a first surface area defined by the propellant and a deterrent applied to a second surface area defined by the first surface area, the second surface area being less than the first surface area. The arrangement is such that the second surface area defines a deterrent free third surface area of the propellant. A primer is operatively disposed relative to the third surface area such that when the primer is activated, the third surface area of the propellant is ignited. The arrangement is such that firstly, while the third surface area is burning and generating gas between the upstream end of the gun barrel and the projectile, the rate of gas pressure increase begins to propel the projectile towards the downstream end of the gun barrel. Secondly, the third surface area of the propellant while burning exposes a progressively increasing surface area of the propellant for burning together with an associated increased generation of gas, the increasing surface area of the propellant defining a concave crater, the crater having a wall which progressively increases in surface area during the burning such that the rate of increase in gas pressure continues to increase for accelerating the projectile towards the downstream end of the gun barrel.